Organic electroluminescent device based on pyrene derivatives

ABSTRACT

A pyrene based compound and its use in an organic light emitting device (OLED) according to the following formula: 
                 
 
In the above formula, Z 1  represents a hydrogen atom, deuterium atom, oxygen atom, silicon atom, selenium atom, substituted or unsubstituted aryl group, substituted or unsubstituted heteroaryl group, substituted or unsubstituted aryl amine or a combination thereof, and Z 2  represents a hydrogen or deuterium atom. One of Y 1  and Y 2  represents a hydrogen atom, deuterium atom, oxygen atom, silicon atom, selenium atom, a substituted or unsubstituted aryl group, substituted or unsubstituted heteroaryl group, substituted or unsubstituted aryl amine or a combination thereof, and the other of Y 1  and Y 2  represents a hydrogen or deuterium atom. X 1  through X 6  independently represent hydrogen atoms, deuterium atoms, alkyl groups or aryl groups, and at least one of X 1  through X 6  represents a bulky alkyl group or bulky aryl group. Also, at least one of X 1  through X 6 , Y 1 , Y 2 , Z 1 , and Z 2  represents a deuterium atom. The pyrene based compounds of this invention are useful in emissive layers, hole transport layers, or electron transport layers of an organic light emitting device (OLED). Within these layers, the pyrene based compound can serve directly to constitute the layers or as a host and/or dopant.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to pyrene based compounds and materialsand their use in organic light emitting devices. These pyrene basedcompounds and materials can be used as the emissive layer, electrontransport layer, hole transport layer or one or more of such layers,although their use as a blue emissive layer is preferred. Thesecompounds can also be used as a host or dopant material for one or moreof such layers.

2. Description of the Related Art

Organic light emitting devices (OLEDS) typically comprise a layer ofemissive material between an anode and a cathode. When a bias is appliedacross the electrodes, positive charges (holes) and negative charges(electrons) are respectively injected from the anode and cathode intothe emissive layer. The holes and the electrons form excitons in theemissive layer to emit light.

Electrodes are chosen to facilitate charge injection. A transparentindium-tin-oxide (ITO) anode has a relatively high work function and istherefore suitable for use as a hole injection electrode, while low workfunction metals such as Al, Mg and Ca are suitable for injection ofelectrons.

To improve the power efficiency of an OLED, it is frequently desirableto enhance charge injection at the electrode interface. Hole transportlayers and electron transport layers may be added adjacent to therespective electrodes to facilitate charge transfer. Depending uponwhether hole transport or electron transport is favored, the lightemissive layer may be located closer to the anode or the cathode. Insome instances, the emissive layer is located within the hole transportor electron transport layer.

Improved performance can be obtained if blocking layers are provided toblock against the injection of either holes or electrons from theadjoining layer and their subsequent escape from the device. Likewise, amodifying layer may be used to improve the contact with one or both ofthe electrodes, or to improve the interface between two other layers.

Some of these layers can be combined. For example, a double-layeredstructure is fabricated from a combined hole-injecting and transportinglayer together with a combined electron-transporting and light-emittinglayer. Likewise, a triple-layered structure is composed of ahole-injecting and transporting layer, a light-emitting layer, and anelectron-injecting and transporting layer.

Hole transport layers may include triarylamnine-based materials,although many other hole transport materials are known. Likewise, analuminum quinolinolate complex known as AlQ₃ is a well knownelectron-transport material which has been used in OLEDs, although otherelectron transport materials are known.

Emissive materials having widely varied structures are known in the artand are generally selected based on color, brightness, efficiency andlifetime. These emissive materials may themselves also have electrontransport or hole transport characteristics.

In addition, it is possible to form these layers from a “host” materialdoped with another material (the “guest” material) designed to achievethe desired effect of the layer (for example, to achieve a holetransport effect, an electron transport effect, or an emissive effect).In the case of an emissive guest-host system, the host must be able totransfer energy to the guest so that a maximum amount of energycontributes to emission by the guest rather than being absorbed by thehost.

Fused aromatic ring compounds have been used in the layers of organiclight emitting devices. Their advanced pi-delocalization system, highmobility and good photoluminescence are desired qualities for OLEDapplication.

Pyrene is a fused aromatic ring compound. In solution, pyrene fluorescespurple blue, yet in solid state it fluoresces white. This white light isdue to intermolecular aggregation.

Since blue emissive materials are desired, it has been considered toprevent aggregation in pyrene by attaching pyrene to a benzene ring atthe 1, 3, and 5 position to make 1,3,5-tripyrene benzene (3TPB), asfollows:

This arrangement results in a good blue emissive material with a peakemission at 450 nm. However, closer investigation of 3TPB reveals thatthe compound still has a minor aggregation problem in its solid state,resulting in a shoulder emission at 482 nm and reduced blue colorpurity.

There continues to be a need for OLED materials exhibiting thermalstability, having bright, high purity luminescent emission, and formaterials which contribute to greater luminescence per injected charge.There is particularly a need for OLED materials which provide a goodblue emission.

SUMMARY OF THE INVENTION

As noted above, pyrene based materials are capable of producing blueemissions that have good color purity. However, due to the tendency toaggregate, the blue emission of these materials is tainted by emissionsof other wavelengths.

It is an object of the present invention to provide a pyrene basedmaterial for OLED application which will have reduced aggregationproblems and, hence, improved blue emission purity.

Thus, in one aspect, the invention is a pyrene based compound accordingto the following general formula (1):

-   -   wherein Z₁ represents a hydrogen atom, deuterium atom, oxygen        atom, silicon atom, selenium atom, substituted or unsubstituted        aryl group, substituted or unsubstituted heteroaryl group,        substituted or unsubstituted aryl amine or a combination        thereof, and Z₂ represents a hydrogen or deuterium atom;    -   wherein one of Y₁ and Y₂ represents a hydrogen atom, deuterium        atom, oxygen atom, silicon atom, selenium atom, a substituted or        unsubstituted aryl group, substituted or unsubstituted        heteroaryl group, substituted or unsubstituted aryl amine or a        combination thereof, and the other of Y₁ and Y₂ represents a        hydrogen or deuterium atom;    -   wherein X₁ through X₆ independently represent hydrogen atoms,        deuterium atoms, alkyl groups or aryl groups, and at least one        of X₁ through X₆ represents a bulky alkyl group or bulky aryl        group; and    -   wherein at least one of X₁ through X₆, Y₁, Y₂, Z₁, and Z₂        represents a deuterium atom.

In one embodiment of the present invention, Z₁, Y₁ and Y₂ independentlyrepresent hole injection chromophores, electron injection chromophores,or both. Z₁, Y₁ and Y₂ independently may also represent a cross-linkinggroup. Preferably, the cross-linking group comprises a di-vinyl group.Finally, Z₁, Y₁ and Y₂ independently may represent a benzene ringsubstituted with one or two pyrenyl groups.

Optionally, X₁ through X₅ independently represent a tert-butyl group ora triphenyl silane.

In a preferred embodiment, both X₂ and X₅ represent a bulky alkyl groupor bulky aryl group and more preferably, the same bulky alkyl or bulkyaryl group.

The following structures are examples of the pyrene based compounds ofthe present invention.

Another aspect of the present invention is an OLED in which at least oneorganic layer is sandwiched between an anode and a cathode, and in whichthe organic layer includes a pyrene based compound as described above.The organic layers of an OLED in which the compound can be used includea hole transport layer, an electron transport layer or an missive layer.

In an emissive layer, the pyrene based compound can be used directly asthe emissive layer or can be used as a host material for an emissivedopant in a case where the emissive layer comprises a pyrene based hostplus an emissive dopant. The emissive dopant can also be the pyrenebased compound described above. Preferably, the emissive layer emits inblue wavelengths.

Alternatively, the pyrene based compound can be used directly as thehole can form a charge transport host material in a case where thecharge transport layer comprises a host material plus a charge transportdopant.

Optionally, the OLEDs of the present invention contain a pyrene basedcompound wherein Z₁, Y₁ and Y₂ independently represent hole injectionchromophores, electron injection chromophores, or both.

This brief summary has been provided so that the nature of the inventionmay be understood quickly. A more complete understanding of theinvention can be obtained by reference to the following detaileddescription of the preferred embodiment thereof in connection with theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a three layer organiclight emitting device.

FIG. 2 is a schematic cross-sectional view of a single layer organiclight emitting device.

DETAILED DESCRIPTION OF THE INVENTION

The pyrene based compound of the present invention has the followinggeneral formula (I):

-   -   wherein Z₁ represents a hydrogen atom, deuterium atom, oxygen        atom, silicon atom, selenium atom, substituted or unsubstituted        aryl group, substituted or unsubstituted heteroaryl group,        substituted or unsubstituted aryl amine or a combination        thereof, and Z₂ represents a hydrogen or deuterium atom;    -   wherein one of Y₁ and Y₂ represents a hydrogen atom, deuterium        atom, oxygen atom, silicon atom, selenium atom, a substituted or        unsubstituted aryl group, substituted or unsubstituted        heteroaryl group, substituted or unsubstituted aryl amine or a        combination thereof, and the other of Y₁ and Y₂ represents a        hydrogen or deuterium atom;    -   wherein X₁ through X₆ independently represent hydrogen atoms,        deuterium atoms, alkyl groups or aryl groups, and at least one        of X₁ through X₆ represents a bulky alkyl group or bulky aryl        group; and    -   wherein at least one of X₁ through X₆, Y₁, Y₂, Z₁, and Z₂        represents a deuterium atom.

In one embodiment of the present invention, Z₁, Y₁ and Y₂ independentlyrepresent hole injection chromophores, electron injection chromophores,or both. Z₁, Y₁ and Y₂ independently may also represent a cross-linkinggroup. Preferably, the cross-linking group comprises a di-vinyl group.Finally, Z₁, Y₁ and Y₂ independently may represent a benzene ringsubstituted with one or two pyrenyl groups.

Optionally, X₁ through X₆ independently represent a tert-butyl group ora triphenyl silane.

In a preferred embodiment, both X₂ and X₅ represent a bulky alkyl groupor bulky aryl group and more preferably, the same bulky alkyl or bulkyaryl group.

A pyrene based compound expressed according to the above formula can bemade with methods known in the art.

Some preferred pyrene based compounds represented by the above formulainclude:

A characteristic of a pyrene based compound expressed according to theabove formula is reduced intermolecular aggregation as compared to 3TPB,due to the substitution of bulky substituent groups. Such a pyrene basedcompound exhibits the quality of a pure blue color without aggregateemission when fluorescing. As a result, an advantage of the disclosedpyrene based materials for use in OLEDs according to the invention isthat they emit a good blue hue without white photoluminescence.

The pyrene based compound expressed according to the above formula canbe used in the hole transport layer, electron transport layer oremissive layer of an OLED.

An OLED may be a multi-layer device, such as a three layer device, shownin FIG. 1, as described more fully below, or a single layer device,shown in FIG. 2.

In FIG. 1, a three layer device comprises an emissive layer 103sandwiched between an electron transport layer 105 and a hole transportlayer 102. Additionally, an electron transport layer 105 and holetransport layer 102 are sandwiched between a cathode 106 and an anode101.

Various procedures for the fabrication of an OLED exist, including thefollowing general procedure: To construct a three layer device, as inFIG. 1, a clean substrate coated with a patterned layer of indium tinoxide (ITO) is first obtained. Next, the substrate is treated with O₂plasma for 1-5 minutes. Afterwards, the substrate is placed in a thermalevaporator and the pressure is lowered. Then, organic and metalliclayers are evaporated onto the substrate at a rate approximately between1-3 Å/s. These organic and metallic layers may vary depending upon thedesired OLED. A hole transport layer 102 is usually evaporated with athickness of ˜200 Å. Next, an emissive layer 103 is evaporated, usuallywith a host and dopant. Normally, 100-400 Å of the emissive layer isdeposited. Then, an electron transport material is evaporated to form alayer 105 that is usually 200-400 Å thick. After the evaporation of thepreferred organic and metallic layers, a mask is placed adjacent to thelayer to define where metal areas corresponding to cathodes are to beevaporated. Then, about 120 Å of a Li-Al alloy is evaporated to improveelectron injection into the device. Finally, after about 1500 Å of Al isdeposited, the evaporator is allowed to cool.

Fabrication of a suitable hole transport, electron transport or emissivelayer using the pyrene based compound can be accomplished through theuse of thermal deposition in a vacuum, or by spin coating of a solutionthereof.

In FIG. 2, a single layer device comprises a combined layer 203,comprising an emissive layer and an electron transport or hole transportlayer, sandwiched between a cathode 206 and an anode 201.

For either a multi-layer device or a single layer device, in theemissive layer, the pyrene based compound can be used directly as theemissive layer or can as a host material for an emissive dopant in acase where the emissive layer comprises a pyrene based host plus anemissive dopant. The emissive dopant can also be the pyrene basedcompound described above.

Alternatively, the pyrene based compound can be used directly as thehole transport layer, the electron transport layer, or both.Furthermore, the pyrene based compound can form a charge transport hostmaterial in the case where the charge transport layer comprises a hostmaterial plus a charge transport dopant.

It is to be understood that the invention is not limited to theabove-described embodiments and that various changes and modificationsmay be made by those of ordinary skill in the art without departing fromthe spirit and scope of the invention.

1. A pyrene based compound according to the following formula:

wherein Z₁ represents a hydrogen atom, deuterium atom, oxygen atom,silicon atom, selenium atom, substituted or unsubstituted aryl group,substituted or unsubstituted heteroaryl group, substituted orunsubstituted aryl amine or a combination thereof, and Z₂ represents ahydrogen or deuterium atom; wherein one of Y₁ and Y₂ represents ahydrogen atom, deuterium atom, oxygen atom, silicon atom, selenium atom,a substituted or unsubstituted aryl group, substituted or unsubstitutedheteroaryl group, substituted or unsubstituted aryl amine or acombination thereof, and the other of Y₁ and Y₂ represents a hydrogen ordeuterium atom; wherein X₁ through X₆ independently represent hydrogenatoms, deuterium atoms, alkyl groups or aryl groups, and at least one ofX₁ through X₆ represents a tert-butyl group; wherein at least one of X₁through X₆, Y₁, Y₂, Z₁ and Z₂ represents a deuterium atom; and whereinZ₁ and one of Y₁ and Y₂ independently represent a hole injectionchromophore, an electron injection chromophore, or both.
 2. A pyrenebased compound according to the following formula:

wherein Z₁ represents a hydrogen atom, deuterium atom, oxygen atom,silicon atom, selenium atom, substituted or unsubstituted aryl group,substituted or unsubstituted heteraoryl group, substituted orunsubstituted aryl amine or a combination thereof, and Z₂ represents ahydrogen or deuterium atom; wherein one of Y₁ and Y₂ represents ahydrogen atom, deuterium atom, oxygen atom, silicon atom, selenium atom,a substituted or unsubstituted aryl group, substituted or unsubstitutedheteroaryl group, substituted or unsubstituted aryl amine or acombination thereof, and the other of Y₁ and Y₂ represents a hydrogen ordeuterium atom; wherein X₁ through X₆ independently represent hydrogenatoms, deuterium atoms, alkyl groups or aryl groups, and at least one ofX₁ through X₆ represents a tert-butyl group; wherein at least one of X₁through X₆, Y₁, Y₂, Z₁ and Z₂ represents a deuterium atom; and whereinZ₁ and one of Y₁ and Y₂ independently represent a cross-linking group.3. The compound of claim 2, wherein the cross-linking group comprises adi-vinyl group.
 4. A pyrene based compound according to the followingformula:

wherein Z₁ represents a hydrogen atom, deuterium atom, oxygen atom,silicon atom, selenium atom, substituted or unsubstituted aryl group,substituted or unsubstituted heteroaryl group, substituted orunsubstituted aryl amine or a combination thereof, and Z₂ represents ahydrogen or deuterium atom; wherein one of Y₁ and Y₂ represents asubstituted aryl group, and the other of Y₁ and Y₂ represents a hydrogenor deuterium atom; wherein X₁ through X₆ independently representhydrogen atoms, deuterium atoms, alkyl groups or aryl groups, and atleast one of X₁ through X₆ represents a tert-butyl group; wherein atleast one of X₁ through X₆, Y₁, Y₂, Z₁, and Z₂ represents a deuteriumatom; and wherein Z₁ and one of Y₁ and Y₂ independently represent abenzene ring substituted with one or two pyrenyl groups.
 5. A pyrenebased compound according to the following formula:

wherein Z₁ and Z₂ independently represent hydrogen atoms; wherein one ofY₁ and Y₂ represents a substituted aryl group, and the other of Y₁ andY₂ represents a hydrogen atom; wherein X₁, X₃, X₄ and X₆ independentlyrepresent deuterium atoms, and X₂ and X₅ independently representtert-butyl groups; and wherein the compound has the following structure:


6. A pyrene based compound according to the following formula:

wherein Z₁ and Z₂ independently represent deuterium atoms; wherein oneof Y₁ and Y₂ represents a substituted aryl group, and the other of Y₁and Y₂ represents a deuterium atom; wherein X₁, X₃, X₄ and X₆independently represent deuterium atoms, and X₂ and X₅ independentlyrepresent tert-butyl groups; and wherein the compound has the followingstructure:


7. A pyrene based compound according to the following formula:

wherein Z₁ and Z₂ independently represent hydrogen atoms, wherein one ofY₁ and Y₂ represents a substituted aryl group, and the other of Y₁ andY₂ represents a deuterium atom; wherein X₁, X₃ X₄ and X₆ independentlyrepresent deuterium atoms, and X₂ and X₅ independently representtert-butyl groups; and wherein the compound has the following structure:


8. A pyrene based compound according to the following formula:

wherein Z₁ and Z₂ independently represent hydrogen atoms; wherein one ofY₁ and Y₂ represents a substituted aryl group, and the other of Y₁ andY₂ represents a hydrogen atom; wherein X₁, and X₃, X₄ and X₆independently represent deuterium atoms, and X₂ and X₅ independentlyrepresent tert-butyl groups; and wherein the compound has the followingstructure:


9. A pyrene based compound according to the following formula:

wherein Z₁ represents a substituted aryl amine group, and Z₂ representsa hydrogen atom; wherein one of Y₁ and Y₂ represents a substituted arylgroup, and the other of Y₁ and Y₂ represents a hydrogen atom; whereinX₁, X₃ and X₆ independently represent hydrogen atoms X₂ and X₅independently represent tert-butyl groups and X₄ represents a deuteriumatom; and wherein the compound has the following structure.


10. A pyrene based compound according to the following formula:

wherein Z₁ and Z₂ independently represent hydrogen atoms; wherein one ofY₁ and Y₂ represents a substituted aryl group and substituted heteroarylgroup combination, and the other of Y₁ and Y₂ represents a hydrogenatom; wherein X₁, X₃, X₄ and X₆ independently represent deuterium atoms,and X₂ and X₅ independently represent tert-butyl groups; and wherein thecompound has the following structure:


11. A pyrene based compound according to the following formula:

wherein Z₁ and Z₂ independently represent hydrogen atoms; wherein one ofY₁ and Y₂ represents a silicon atom and substituted aryl groupcombination, and the other of Y₁ and Y₂ represents a hydrogen atom;wherein X₁, X₃, X₄ and X₆ independently represent deuterium atoms, andX₂ and X₅ independently represent tert-butyl groups; and wherein thecompound has the following structure:


12. A pyrene based compound according to the following formula:

wherein Z₁ and Z₂ independently represent hydrogen atoms; wherein one ofY₁ and Y₂ represents a substituted aryl group, and the other of Y₁ andY₂ represents a hydrogen atom; wherein X₁, X₃, X₄ and X₆ independentlyrepresent deuterium atoms, and X₂ and X₅ independently representtert-butyl groups; and wherein the compound has the following structure:


13. A pyrene based compound according to the following formula:

wherein Z₁ and Z₂ independently represent hydrogen atoms; wherein one ofY₁ and Y₂ represents a substituted aryl group, and the other of Y₁ andY₂ represents a hydrogen atom; wherein X₁, X₃, X₄ and X₆ independentlyrepresent deuterium atoms, and X₂ and X₅ independently representtert-butyl groups; and wherein the compound has the following structure:


14. A pyrene based compound according to the following formula:

wherein Z₁ and Z₂ independently represent hydrogen atoms; wherein one ofY₁ and Y₂ represents an oxygen atom and substituted aryl groupcombination, and the other of Y₁ and Y₂ represents a hydrogen atom;wherein X₁, X₃, X₄ and X₆ independently represent deuterium atoms, andX₂ and X₅ independently represent tert-butyl groups; and wherein thecompound has the following structure:


15. An organic light emitting device comprising an anode, a cathode andat least one organic layer sandwiched between the anode and the cathode,wherein the organic layer comprises a pyrene based compound of thefollowing general formula:

wherein Z₁ represents a hydrogen atom, deuterium atom, oxygen atom,silicon atom, selenium atom, substituted or unsubstituted aryl group,substituted or unsubstituted heteroaryl group, substituted orunsubstituted aryl amine or a combination thereof, and Z₂ represents ahydrogen or deuterium atom; wherein one of Y₁ and Y₂ represents ahydrogen atom, deuterium atom, oxygen atom, silicon atom, selenium atom,a substituted or unsubstituted aryl group, substituted or unsubstitutedheteroaryl group, substituted or unsubstituted aryl amine or acombination thereof, and the other of Y₁ and Y₂ represents a hydrogen ordeuterium atom; wherein X₁ through X₆ independently represent hydrogenatoms, deuterium atoms, alkyl groups or aryl groups, and at least one ofX₁ through X₆ represents a tert-butyl group; and wherein at least one ofX₁ through X₆, Y₁, Y₂, Z₁, and Z₂ represents a deuterium atom.
 16. Theorganic light emitting device of claim 15, wherein the organic layer isan emissive layer, a hole transport layer, an electron transport layeror combinations thereof.
 17. The organic light emitting device of claim15, wherein the pyrene based compound serves as a host material of saidorganic layer.
 18. The organic light emitting device of claim 15,wherein the pyrene based compound serves as a dopant of said organiclayer.
 19. The organic light emitting device of claim 15, wherein Z₁ andone of Y₁ and Y₂ independently represent a hole injection chromophore,an electron injection chromophore, or both.
 20. The organic lightemitting device of claim 15, wherein Z₁ and one of Y₁ and Y₂independently represent a cross-linking group.
 21. The organic lightemitting device of claim 20, wherein the cross-linking group comprises adi-vinyl group.
 22. The organic light emitting device of claim 15,wherein Z₁ and one of Y₁ and Y₂ independently represent a benzene ringsubstituted with one or two pyrenyl groups.
 23. The organic lightemitting device of claim 15, wherein the pyrene based compound has thefollowing structure:


24. The organic light emitting device of claim 15, wherein the compoundhas the following structure:


25. The organic light emitting device of claim 15, wherein the pyrenebased compound has the following structure:


26. The organic light emitting device of claim 15, wherein the pyrenebased compound has the following structure:


27. The organic light emitting device of claim 15, wherein the pyrenebased compound has the following structure:


28. The organic light emitting device of claim 15, wherein the pyrenebased compound has the following structure:


29. The organic light emitting device of claim 15, wherein the pyrenebased compound has the following structure:


30. The organic light emitting device of claim 15, wherein the pyrenebased compound has the following structure:


31. The organic light emitting device of claim 15, wherein the pyrenebased compound has the following structure:


32. The organic light emitting device of claim 15, wherein the pyrenebased compound has the following structure:


33. The organic light emitting device of claim 15, wherein the pyrenebased compound has the following structure: